1. Field of the Invention
The present invention relates to a method for estimating a tire wear life, and more particularly, to a method for estimating a tire wear life which enables estimating the tire wear lie or the degree of wear of rubber in actual use.
2. Description of the Related Art
Heretofore, the wear life of a tire used for vehicles has been estimated from the condition of wear (the degree of wear or the amount of wear) after a vehicle mounting the tire whose wear life is to be estimated is actually driven for a specific distance (as for the definition of the word "wear life", refer to page 13 of the specification).
However, this method has a drawback in that the test is quite time-consuming because the distance to be driven by the vehicle for the test must be great in order to get an accurate measurement of the amount of wear of the tire required for a highly precise estimation.
To overcome the above drawback, in the technology disclosed in Japanese Patent Application Publication (hereinafter, referred to as JP-B) 1-56374, at least two pairs of test tires are mounted to a vehicle used for the test and are driven on roads in a manner such that the rotation speeds of the two tires are different between the pairs by a desired extent so that the wear of the tire due to the driving force and due to the braking force can be evaluated simultaneously.
As the formula for estimating the amount of wear of a tire, Schallamach's formula of the amount of wear is known. In accordance with this theoretical formula, the amount of wear M of a tire per unit distance of driving is considered to be proportional to the friction energy and can be expressed by the following formula (1): EQU M=.gamma..rho.F.sup.2 /C (1)
In formula (1), .gamma. represents the degree of wear of a tire, .rho. represents resilience, F represents an external force applied to the tire and C represents the rigidity of the tire against a force in the longitudinal direction or the transverse direction thereof When the rigidity C is expressed move specifically by the rigidity in the longitudinal direction, (in the driving direction) Cd, and the rigidity in the direction of braking Cb, and the rigidity in the transverse direction Cs, Schallamach's formula of the amount of wear is expressed by the following formula (2): EQU M=.gamma..rho.F.sup.2 /(Cd+Cb+Cs) EQU =.gamma..rho.(Fx+.sup.2 /Cd+Fx-.sup.2 /Cb+Fy.sup.2 /Cs) (2)
In the above formula, Fx+ represents a force in the forward direction generated by a driving force, Fx- represents a force in the backwards direction generated by a braking force and Fy represents an input force in the transverse direction.
However, the technology described in the specification of JP-B 1-56374 has a drawback in that at least one actual road test must be conducted for a long time and thus it still takes a long time to estimate the tire wear life, although the time required for the test can be decreased in comparison with the time required for methods of estimation using only one pair of tires in one run of the road test.
Moreover, Schallamach's formula of the amount of wear has a drawback in that, although the formula takes rigidities in the direction of driving, in the direction of braking and in the transverse direction into consideration, accurate estimation of tire wear life of a tire mounted to a vehicle in actual use is still difficult when factors taken into consideration are limited to these parameters.
When driving a vehicle in actual use, there are more diverse factors affecting the wear of a tire such as the properties of the rubber of the tire tread portion, tire tread patterns and structures, and input forces experienced by a tire in the actual use of the tire by the customers (during driving in the conditions of actual road use of the vehicle). Therefore, in the actual driving condition of a vehicle which is affected by so many diverse factors, it is obviously difficult to accurately estimate the wear of a tire using Schallamach's formula of the amount of wear in which only rigidities in the direction of driving, in the direction of braking and in the transverse direction are considered.